Numerical prediction of tunnelling-induced settlements in coarse-grained soils

The paper describes the results of a study carried out to analyse the surface settlements induced by the excavation of the Milan underground new line 5 by an earth pressure balance (EPB) machine in granular soils. Settlements measured during the construction under green-field conditions are presented and interpreted using the classical Gaussian empirical prediction and are compared to numerical predictions obtained by finite element calculations performed with the software Plaxis 2D. A simple linear elastic-perfectly plastic Mohr-Coulomb model (MC) and the more advanced Hardening Soil with small strain model (HSsmall) were adopted for the description of the soil behaviour. It was observed a very good agreement between the numeri-cal solution obtained using the HSsmall constitutive model and the monitoring data. On the contrary, the pre-diction computed using the MC model was found to highly underestimate the maximum settlement and to produce a much wider subsidence curve than the empirical ones